The present invention relates generally to a system and a process for improving the quality of gasification slag product. More particularly, the present invention relates to systems and processes for improving the quality of the slag product from a gasification process that converts a carbonaceous feedstock into desirable gaseous products such as synthesis gas.
The product of gasification is a reactive gas predominantly comprising carbon monoxide and hydrogen. This gas can be used as a fuel gas, or it can be chemically converted to other products, such as synthetic oil. During gasification, the inorganic portion of the coal forms a vitreous slag by-product, which comprises molten or partially-fused particles that come into contact with the furnace wall, flow downwards towards the bottom opening, or taphole, of the furnace, then out of the furnace. The slag then drops into a water bath where it is quenched, solidified, and broken up into a granular aggregate material. Typically, slag is removed from the water bath as a slurry.
Often, the slag produced as a byproduct of gasification processes does not meet market expectations, mainly because of high residual carbon content. Carbon content of the slag is often between 20-30%, sometimes as high as 70%, while less than 5% is normally required for the slag to be commercially marketable. Slag with a low carbon content can be used as aggregate for road or construction fill, concrete mix, roofing shingles, as sandblasting grit or for other applications.
Various processing methods have been instituted to improve slag quality and increase its marketability, such as the screening technology disclosed in U.S. Pat. No. 7,328,805, (incorporated herein by reference). However, some slag products may not present a certain size fraction showing the carbon content is predominant, and the above mentioned screening method is not beneficial for such slag.
Accordingly, there is a need for new technology that can improve the quality of slag product produced during gasification of carbonaceous feedstocks, such that the resulting slag product is marketable.